Using 3 ports, this rectangular oscillator was found in the March 1996 issue of Electronics Now magazine. The maximum frequency is a few megahertz, determined by R1 and C1.
This circuit indicates when a 28 V lamp burns, lighting a neon lamp with higher voltage. The...
This circuit, which can be used on an optical link, is suggested by the Texas Instruments...
We found this circuit in a 1992 Popular Electronics. The circuit has an optical sensor with LED...